Traditionally, lime blended with sodium sulfide is used to remove wool and hair and dissolve these into a pulp. Additionally, this process opens the fiber structure and plumps the hide due to alkalinity. The duration of the process may vary from 18 hours to 7 days depending upon the method employed. This process is responsible for the major parts of the COD load from a tannery due to the chemicals include −2 to 10% lime and 1 to 4% sodium sulfide. The water polluted with these chemicals and the solubilized hair leads to an increase in alkalinity, organic nitrogen, BOD, COD and TDS. There will be air pollution with hydrogen sulfide and the solid wastes with hair pulp, lime and organic matter forming sludge.
Conventionally, lime in combination with sodium sulfide has been used for the unhairing of hides/skins. For hair loosening and opening up, enzymes that remain sufficiently stable in alkaline pH are also used in addition to lime and sulfide. This later method of operation generally takes place in the pH range from 9–12. Both lime and sulfide and its enzyme supported unhairing process result in the discharge of effluent with high TDS (total dissolved solids) and increased pH that pollutes the soil as well as the ground water and therefore cause irreversible damage to the ecosystem.
Since the discovery of the enzymatic unhairing process in 1910 by Otto Rohm (German Patent No. 268-873), considerable amount of work has been carried out and G. H. Green has given a notable review ((J. Soc. Leather Traders Chemists, 36, 217–232, 1952).
The use of proteases in different partial operations in the beam house has been proposed and also realized in practice. [Cf. E. P fleiderer and R. Reiner in Biotechnology, Editor H. J. Rehm, pp. 729–743, VCH 1988]. In addition, amylases, particularly in combination with proteases, have similarly found an entry into bating operation of the beam house (U.S. Pat. No. 4,273,876).
Most of these enzymes used in beam house operation are of microbial origin. Apart from the microbial enzymes, enzymes of animal origin have also been reported (Christner et al, 1992, U.S. Pat. No. 5,102,422) for the purpose of bating.
The concurrent use of lipase and amylases (in the form of pancreatin) in the presence of desoxycholic acid is known from Hungarian patent 33 25 (Chem. Abstr. 77, 7341K).
Monsheimer et al 1981 (U.S. Pat. No. 4,273,876) have disclosed a method for the enzymatic bating of pelts with simultaneous removal of scud in acid pH range in the presence of an amylase and a protease of either microbial or pancreatic origin.
Sorenson et al (WO 90/12118) have disclosed a method for unhairing of skins/hides with an aqueous float with a pH value of 3.5–5.0 and containing an organic acid and a special carbohydrase.
The purification and characterization of proteases from Calotropis gigantean have been reported by K. I. Abraham and P. N. Joshi. (Biochimica Biophysica Acta, 568, 111–119, and 120–126, 1979).
The purification and properties of the enzyme from Carica papaya have been reported by A. K. Balls, H. Lineweaver and R. R. Thomson (Science, 86, p379, 1937) and A. K. Balls and H. Lineweaver (Journal of Biological Chemistry, 130, p669, 1939).
However, the formulations of these enzymes with suitable treatment to impart stability and storability for the application in industries have not been reported so far. Therefore, to avoid expensive purification processes, the inventors have extracted the crude enzyme and processed it by adding suitable buffer, glycerol and preservative with a view to keep the total activity of the enzyme intact.
The proteolytic enzymes of pancreas have been reported by K. A. Walsh (in Methods in Enzymology, vol 19, 41–63, 1970). The proteolytic enzyme trypsin and its inactive precursor trypsinogen were first obtained in crystalline form from bovine pancreatic tissue by Northrop, J. H., Kunitz, M. and Herriot, R. M. (Crystalline Enzymes, second edition, Columbia University Press, New York, 1948). The inactive trypsinogen is transformed into active trypsin by trypsin itself or by calcium ions.
The cited enzyme formulation of U.S. Pat. No. 5,102,422 contains not only the enzymes of microbial and plant origins and also it has many organic compounds that the applicants have not used in this present invention. The enzyme formulation (U.S. Pat. No. 5,102,422) requires lime for its activity. The distinguished property of enzymes of the present invention is that it does not require lime or sulfide for depilation.
Additionally, enzymes of the present invention, essentially removes the hair along with the epidermal layer which leaves the pelt scud free and white in colour. This provides a process that leaves the hair in an intact form.
The same enzymes of the present invention could also be used in the recovery of value added products from biowastes of leather industry for various applications, for e.g., hydrolysis of chrome shavings and fleshing etc.
In the process of unhairing, both the lime and sulfide and its enzyme supported processes result in the discharge of effluent with high TDS, alkalinity, sulfide, organic nitrogen and ammonia. Besides, these processes are responsible for the major part of BOD and COD load, mainly due to the chemicals that include calcium hydroxide and sodium sulfide.
The inventions thus far reported claim to have enzymes for unhairing in the presence of lime or lime and sulfide system or acids. Secondly, the enzyme solution containing herbal (plant) enzymes in leather processing have not been reported so far.
The enzyme preparations containing pancreatic enzymes have been reported to be useful only for bating and degreasing. Several organic solvents have been reportedly used in the enzyme preparation. These may have adverse effects on the public health and environment particularly at the application level. Moreover, the enzymes that depend mostly on structural organizations for their activity have the tendency of denaturation by organic solvents like any other proteins.
The purification and characterization of proteases from Calotropis gigantea have been reported by K. I. Abraham and P. N. Joshi (Biochimica et Biophysica Acta, 568, 111–119, 120–126, 1979). The purification and properties of the enzymes isolated from Carica papaya have been reported by A. K. Balls and H. Lineweaver (Journal of Biological Chemistry, 130, p 669, 1939). However, the formulations of these enzymes with suitable treatment to impart stability and storability for the application in industries have not been reported so far. Therefore, to avoid the expensive purification processes, the applicants have extracted the crude enzyme and processed it by adding suitable buffer, glycerol and preservative with a view to keep the total activity of the enzyme intact.
The proteolytic enzymes of pancreas have been reported by K. A. Walsh (in Methods in Enzymology, vol 19, 41–63, 1970). The proteolytic enzyme trypsin and its inactive precursor, trypsinogen were first obtained in crystalline form from bovine pancreatic tissue by Northrop, J. H., Kunitz, M and Herriot R. M. (Crystalline Enzymes, second edition, Columbia University Press, New York, 1948). The inactive trypsinogen is transformed into active trypsin by trypsin itself or by calcium ions.
Use of many chemicals and solvents in the prior art products (U.S. Pat. Nos. 5,102,422 and 5,525,509) may lead to a number of leather imperfections. The methods followed are also cumbersome and cost defective due to power and water consumption.
The enzyme carriers, such as Bentonite and kaolines, used in the prior art products at the unhairing stage further contribute to increase the TDS of the effluent.
However, no animal enzymes have been reported so far for unhairing in the absence of lime and/or lime and sulfide system or acids. Additionally, the enzymatic unhairing and bating occurring in a single step has also not been reported yet.
The main objective of the present invention is to provide a novel process for total lime—sulfide free unhairing in skins/hides using animal and/or herbal (plant) enzymes to solve the problems caused by lime or lime and sulfide or lime and sulfide aided enzymatic method of leather processing.
Another objective of the present invention is to minimize/avoid water and power consumption and reduces the effluent volume drastically.
Yet another objective of the present invention is to use an enzyme solution for beam house operation that is stable even up to 60° C. for at least 6 weeks without losing its activity.
Still another objective of this invention is to use an enzyme solution that is economically and ecologically acceptable for use in leather processing.
Still yet another objective of this invention is to evolve an enzymatic process wherein both lime, lime and sulfide free unhairing and bating taking place simultaneously.
Yet another objective of this invention is to recover the whole hair in its native state as it appears on the animal for its further utilization and to reduce the BOD and COD levels of the effluent discharged.
Still yet another objective of this invention is to remove the hair along with the epidermal layer to obtain scud free white pelt, which is uncommon in other enzymatic or non-enzymatic methods of unhairing.